The function of the osphradium, a structure within the mantle cavity of many molluscs, has been the subject of some speculation. It is generally accepted to be a sense organ, but the modality to which it is sensitive remains obscure. Two major theories have been proposed. The first is that it is a chemoreceptor involved in food location. Copeland1, Wölper2 and Brown and Noble3 have shown, by means of behavioural studies, that certain species of carnivorous gastropod depend on an intact osphradium and associated nerve supply for their ability to follow the chemical trail emanating from food material. Extirpation of the organ or section of the innervation leads to the loss of this attribute.